Heat-exchanger assemblies are employed in a wide variety of applications, with one application being use as an intercooler for turbo-charged or super-charged internal combustion engines. In the case of a turbocharger, at least one rotary compressor wheel is driven by the exhaust gas of the engine, while in the case of a supercharger, at least one rotary compressor wheel is driven mechanically, usually by the rotary output of the engine. In either case, the compressor wheel is employed to compress and elevate the pressure of ambient air prior to induction into the engine to support combustion. By compression of the intake air, a given volume of air will have a greater mole content of oxygen than an otherwise equal volume of air at ambient pressure. As a consequence, the additional oxygen permits the combustion of a greater quantity of fuel so that for an engine of a given size, a greater power output can be achieved as a result of the charging of the combustion air.
The efficiency of such air-charging systems can be improved through use of a heat-exchanging arrangement, typically referred to as an intercooling system. Because the ambient air is heated as it is compressed, part of the efficiency derived by employing the combustion air-charging device in the first instance, i.e., the densification of the combustion air supplied to the engine, is lost because a volume of hot, compressed air contains less oxygen than an equal volume of cooler, compressed air, when both are at the same pressure. Thus, for a given pressure, a cooler combustion air charge for an engine permits more power to be developed, compared to the same charge at the same pressure at a higher temperature.
To thus maximize the efficiency of such air-charging systems, intercoolers are employed to cool the compressed air prior to its induction into the engine so as to provide, at any given pressure, a maximum mole content of oxygen.
While heat-exchanging intercoolers for internal combustion engines can be of a generally rectangular-shaped configuration, systems which are desirably compact are generally torodial or doughnut-shaped, and can be fitted about the rotary shaft of the associated air-charging compressor. For such an arrangement, heat-exchanging characteristics of the intercooler are optimized by employing coolant tubes which have a generally wedge-shaped cross-sectional configuration. Such wedge-shaped tubes can be arranged generally parallel to the associated rotating shaft, with flow of air to be cooled passing either radially inwardly or radially outwardly through the torodial intercooler. Examples of such arrangements are disclosed in commonly-assigned, co-pending U.S. patent application Ser. No. 10/251,537, filed Sep. 20, 2002, entitled Internally Mounted Radial Flow Intercooler for a Combustion Air Charger, naming Steven P. Meshenky et al. as inventors, the disclosure of which is hereby incorporated by reference.
In the typical wedge-shaped coolant tube of this type of heat-exchanging intercooler, the minor dimension of the tube increases in a direction along the tube depth or width. If a uniform wall thickness is employed for the wedge-shaped tube, the increased tube minor dimension increases the flow area, resulting in reduced heat-transfer performance.
The present invention contemplates a heat-exchanger assembly having wedge-shaped coolant tubes which are configured to optimize heat-exchanging performance.